Modified cracking catalyst composition

ABSTRACT

A novel catalytic cracking composition comprising a solid cracking catalyst and a diluent containing a selected magnesium compound or a selected magnesium compound in combination with one or more heat-stable metal compounds.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a novel catalyst composition comprising asolid cracking catalyst and a diluent containing a selected magnesiumcompound or a selected magnesium compound in combination with one ormore heat-stable metal compounds.

2. Description of the Prior Art

U.S. Pat. No. 3,944,482 to Mitchell et al. discloses a process directedto the catalytic cracking of hydrocarbon feeds containing metals using afluid catalyst having improved metals tolerant characteristics.Bartholic in U.S. Pat. No. 4,289,605 relates to a process for thecatalytic cracking of hydrocarbon feeds containing metals using acatalyst composition containing a solid cracking catalyst and calcinedmicrospheres (for example, calcined kaolin clay) having a surface areawithin the range of 10 to 15 m² /gram. In our U.S. patent applicationsSer. Nos. 354,163 filed Mar. 3, 1982, for Catalytic CrackingComposition, and 354,162, filed Mar. 3, 1982, for Process for CrackingHigh Metals Content Feedstocks, we have disclosed a novel catalystcomposition comprising a solid cracking catalyst and a diluentcontaining a selected alumina or a selected alumina in combination withone or more heat-stable metal compounds.

SUMMARY OF THE INVENTION

We have found that catalytic cracking of high metals content feedstockssuch as, for example, those containing iron, vanadium, nickel andcopper, can be substantially improved by contacting said charge stocksunder catalytic cracking conditions with a novel catalyst composition,claimed herein, comprising a solid cracking catalyst and a diluentselected from the group consisting of a magnesium compound and amagnesium compound in combination with one or more heat-stable metalcompounds. The improvement resides in the ability of the catalyst systemto function well even when the catalyst carries a substantially highlevel of metal on its surface, for example, up to 5000 ppm of nickel ornickel equivalents, or even higher, or up to 20,000 ppm of vanadium. By"ppm of nickel equivalent" we mean ppm nickel+0.20 ppm vanadium. Thusfeedstocks having very high metals content can be satisfactorily usedherein. The novel process using the novel catalyst composition definedand claimed herein is covered in our U.S. Application Ser. No. 375,379,entitled "Process for Cracking High Metals Content Feedstocks", filedconcurrently herewith.

The cracking catalyst component of the novel catalyst composition usedin the novel process can be any cracking catalyst of any desired typehaving high activity. By "high activity" we mean catalyst of fresh MATActivity above about 1.0, preferably up to about 4.0, or even higher,where ##EQU1##

The "MAT Activity" was obtained by the use of a microactivity test (MAT)unit similar to the standard Davison MAT (see Ciapetta et al., Oil & GasJournal, 65, 88 (1967). All catalyst samples were tested at 900° F.(482° C.) reaction temperature; 15 weight hourly space velocity; 80seconds of catalyst contact time; and a catalyst to oil ratio of 2.9with 2.5 grams of catalyst. The charge stock was a Kuwait gas oil havinga boiling range of 500° F. to 800° F. (260° C. to 427° C.). Inspectionsof this Kuwait gas oil are shown in Table I below.

                  TABLE I                                                         ______________________________________                                        KUWAIT GAS OIL INSPECTIONS                                                    Stock               MAT                                                       Identification      Feedstock                                                 ______________________________________                                        Inspections:                                                                  Gravity, API, D-287 23.5                                                      Viscosity, SUS D2161, 130° F.                                                              94.7                                                      Viscosity, SUS D2161, 150° F.                                                              70.5                                                      Viscosity, SUS D2161, 210° F.                                                              50.8                                                      Pour Point, D97, °F.                                                                       +80                                                       Nitrogen, wt %      0.074                                                     Sulfur, wt %        2.76                                                      Carbon, Res., D524, wt %                                                                          0.23                                                      Bromine No., D1159  5.71                                                      Aniline Point, °F.                                                                         176.5                                                     Nickel, ppm         <0.1                                                      Vanadium, ppm       <0.1                                                      Distillation, D1160 at 760 mm                                                 End Point, °F.                                                                             800                                                       5 Pct. Cond.        505                                                       Approx. Hydrocarbon                                                           Type Analysis: Vol. %                                                         Carbon as Aromatics 23.1                                                      Carbon as Naphthenes                                                                              10.5                                                      Carbon as Paraffins 66.3                                                      ______________________________________                                    

Thus, catalytic cracking catalysts suitable for use herein as hostcatalyst include amorphous silica-alumina catalysts; syntheticmica-montmorillonite catalysts as defined, for example in U.S. Pat. No.3,252,889 to Capell et al.; and cross-linked clays (see, for example,Vaughn et al. in U.S. Pat. Nos. 4,176,090 and 4,248,739; Vaughn et al.(1980), "Preparation of Molecular Sieves Based on Pillared InterlayeredClays"; Proceedings of the 5th International Conference on Zeolites,Rees, L. V., Editor, Heyden, London, pages 94-101; and Lahav et al.,(1978) "Crosslinked Smectites I Synthesis and Properties of HydroxyAluminum Montmorillonite", Clay & Clay Minerals, 26, pages 107-114;Shabtai, J. in U.S. Pat. No. 4,238,364; and Shabria et al. in U.S. Pat.No. 4,216,188).

Preferably, the host catalyst used herein is a catalyst containing acrystalline aluminosilicate, preferably exchanged with rare earth metalcations, sometimes referred to as "rare earth-exchanged crystallinealuminum silicate" or one of the stabilized hydrogen zeolites. Mostpreferably, the host catalyst is a high activity cracking catalyst.

Typical zeolites or molecular sieves having cracking activity which canbe used herein as a catalytic cracking catalyst are well known in theart. Suitable zeolites are described, for example, in U.S. Pat. No.3,660,274 to Blazek et al., or in U.S. Pat. No. 3,647,718 to Hayden etal. The descriptions of the crystalline aluminosilicates in the Blazeket al. and Hayden et al. patents are incorporated herein by reference.Synthetically prepared zeolites are initially in the form of alkalimetal aluminosilicates. The alkali metal ions are exchanged with rareearth metal ions to impart cracking characteristics to the zeolites. Thezeolites are, of course, crystalline, three-dimensional, stablestructures containing a large number of uniform openings or cavitiesinterconnected by smaller, relatively uniform holes or channels. Theeffective pore size of synthetic zeolites is suitably between six and 15A in diameter. The overall formula for the preferred zeolites can berepresented as follows:

    xM.sub.2/n O:Al.sub.2 O.sub.3 :1.5-6.5 SiO.sub.2 :yH.sub.2 O

where M is a metal cation and n its valence and x varies from 0 to 1 andy is a function of the degree of dehydration and varies from 0 to 9. Mis preferably a rare earth metal cation such as lanthanum, cerium,praseodymium, neodymium or mixtures of these.

Zeolites which can be employed herein include both natural and syntheticzeolites. These zeolites include gmelinite, chabazite, dachiardite,clinoptilolite, faujasite, heulandite, analcite, levynite, erionite,sodalite, cancrinite, nepheline, lazurite, scolecite, natrolite,offretite, mesolite, mordenite, brewsterite, ferrierite, and the like.The faujasites are preferred. Suitable synthetic zeolites which can betreated in accordance with this invention include zeolites X, Y, A, L,ZK-4, B, EF, R, HJ, M, Q, T, W, Z, alpha and beta, ZSM-types and omega.The term "zeolites" as used herein contemplates not onlyaluminosilicates but substances in which the aluminum is replaced bygallium or boron and substances in which the silicon is replaced bygermanium.

The preferred zeolites for this invention are the synthetic faujasitesof the types Y and X or mixtures thereof.

To obtain good cracking activity the zeolites have to be in a properform. In most cases this involves reducing the alkali metal content ofthe zeolite to as low a level as possible. Further, a high alkali metalcontent reduces the thermal structural stability, and the effectivelifetime of the catalyst will be impaired as a consequence thereof.Procedures for removing alkali metals and putting the zeolite in theproper form are well known in the art as described in U.S. Pat. No.3,537,816.

The crystalline aluminosilicate zeolites, such as synthetic faujasite,will under normal conditions crystallize as regularly shaped, discreteparticles of approximately one to ten microns in size, and, accordingly,this is the size range normally used in commercial catalysts. Theparticle size of the zeolites can be, for example, from about 0.5 toabout 10 microns but generally from about 1 to about 2 microns or less.Crystalline zeolites exhibit both an interior and an exterior surfacearea, with the largest portion of the total surface area being internal.Blockage of the internal channels by, for example, coke formation andcontamination by metals poisoning will greatly reduce the total surfacearea.

Especially preferred as the catalytically active component of thecatalyst system claimed herein is a crystalline aluminosilicate, such asdefined above, dispersed in a refractory metal oxide matrix, forexample, as set forth in U.S. Pat. No. 3,944,482 to Mitchell et al.,referred to hereinabove.

The matrix material in the host catalyst can be any well-knownheat-stable or refractory metal compounds, for example, metal oxides,such as silica, magnesia, boron, zirconia, or mixtures of thesematerials or suitable large pore clays, cross-linked clays or mixedoxide combinations.

The particular method of forming the catalyst matrix does not form apart of this invention. Any method which produces the desired crackingactivity characteristics can suitably be employed. Large poredrefractory metal oxide materials suitable for use as a matrix can beobtained as articles of commerce from catalyst manufacturers or they canbe prepared in ways well known in the art such as described, forexample, in U.S. Pat. No. 2,890,162, the specification of which isincorporated herein by reference.

The amount of the zeolitic material dispersed in the matrix can suitablybe from about 10 to about 60 weight percent, preferably from about 10 toabout 40 weight percent, but most preferably from about 20 to about 40weight percent of the final catalyst. The method of forming the finalcomposited catalyst also forms no part of this invention, and any methodwell known to those skilled in this art is acceptable. For example,finely divided zeolite can be admixed with the finely divided matrixmaterial, and the mixture spray dried to form the final catalyst. Othersuitable methods are described in U.S. Pat. Nos. 3,271,418; 3,717,587;3,657,154; and 3,676,330; whose descriptions are incorporated herein byreference. The zeolite can also be grown on the matrix material ifdesired, as defined, for example in U.S. Pat. No. 3,647,718 to Hayden etal., referred to above.

The second component of the catalyst system defined herein, as aseparate and distinct entity, is a diluent selected from the groupconsisting of a magnesium compound and a magnesium compound incombination with at least one heat-stable metal compound. By "magnesiumcompound" we mean to include magnesium oxide, attapulgite sepiolite,hectorite, chrysotile and other magnesium-containing clay minerals asdefined by R. E. Grim in "Clay Mineralogy", McGraw, Hill (1968), NewYork, NY. By "combination" we mean that the magnesium compound and theheat-stable metal compound can be combined as a physically discretecomponent. By "heat-stable metal compound" we mean to include metalcompounds that will, under the temperatures existing in a catalyticcracking unit, will not decompose, or if they do decompose, willdecompose to compounds that will remain stable in such environment.Examples of such heat-stable metal compounds are the metal oxides ofsilicon, aluminum, iron, boron, zirconium, calcium, phosphorus andselected clay minerals, as defined by R. E. Grim, referred to above. Theamount of heat-stable compound present can be up to about 90 weightpercent relative to the magnesium compound, although in general, theamount will be up to about 50 weight percent or even higher.

The second component must be carefully selected. In order to obtain thedesired results herein, it is critical that its fresh surface area be inthe range of about 30 to about 1000 m² /gram, preferably about 50 toabout 600 m² /gram. Equally critical is the total pore volume, whichmust be in the range of about 0.05 to about 2.5 cc/gram, preferablyabout 0.05 to about 1.5 cc/gram. It is desirable that the average poreradius be in the range of about 10 to about 200 A, preferably about 20to 100 A. The particle size can vary over a wide range, but generallywill be in the range of about 20 to about 150 microns, preferably about20 to about 90 microns.

The weight ratio of the catalytically active component to the diluent(the second component) can be in the range of about 10:90 to about90:10, preferably in the range of about 50:50 to about 70:30.

The catalyst composition defined above possesses a high tolerance tometals and thus is particularly useful in the cracking of high metalscontent charge stocks. Suitable charge stocks include crude oil,residuums or other petroleum fractions which are suitable catalyticcracking charge stocks except for the high metals contents. A highmetals content charge stock for purposes of this invention is defined asone having a total metals concentration equivalent to or greater than avalue of ten as calculated in accordance with the followingrelationship:

    10[Ni]+[V]+[Fe]≧10

where [Ni], [V] and [Fe] are the concentrations of nickel, vanadium andiron, respectively, in parts per million by weight. The process isparticularly advantageous when the charge stock metals concentration isequal to or greater than 100 in the above equation. It is to beunderstood therefore that the catalyst compositions described above canbe used in the catalytic cracking of any hydrocarbon charge stockcontaining metals, but is particularly useful for the treatment of highmetals content charge stocks since the useful life of the catalyst isincreased. The charge stocks can also be derived from coal, shale or tarsands. Thus charge stocks which have a metals content value of at leastabout 10 in accordance with the above equation cannot be treated as wellas desired economically in commercial processes today due to highcatalyst make-up rates, but can now be treated utilizing the catalystcompositions described and claimed herein. Typical feedstocks are heavygas oils or the heavier fractions of crude oil in which the metalcontaminants are concentrated. Particularly preferred charge stocks fortreatment using the catalyst composition of this invention includedeasphalted oils boiling above about 900° F. (482° C.) at atmosphericpressure; heavy gas oils boiling from about 650° F. to about 1100° F.(343° C. to 593° C.) at atmospheric pressure; atmospheric or vacuumtower bottoms boiling above about 650° F.

The preferred method of operating a process using the catalystcomposition of this invention is by fluid catalytic cracking. Hydrogenis generally not added to the reaction.

A suitable reactor-regenerator for carrying out a process using thecatalyst composition is shown in the attached FIG. I. The crackingoccurs in the presence of the fluidized novel catalyst compositiondefined herein in an elongated reactor tube 10 which is referred to as ariser. The riser has a length to diameter ratio of above 20 or above 25.The charge stock to be cracked is passed through preheater 2 to heat itto about 600° F. (315.6° C.) and is then charged into the bottom ofriser 10 to the end of line 14. Steam is introduced into oil inlet line14 through line 18. Steam is also introduced independently to the bottomof riser 10 through line 22 to help carry upwardly into the riserregenerated catalyst which flows to the bottom of the riser throughtransfer line 26.

The oil charge to be cracked in the riser is, for example, a heavy gasoil having a boiling range of about 650° F. to about 1100° F. (343° to593° C.). The steam added to the riser can amount to about 10 weightpercent based on the oil charge, but the amount of steam can varywidely. The catalyst employed is the novel catalyst composition definedabove in a fluid form and is added to the bottom of the riser. The risertemperature range is suitably about 900° F. to about 1100° F. (482° C.to 593° C.) and is controlled by measuring the temperature of theproduct from the riser and then adjusting the opening of valve 40 bymeans of temperature controller 42 which regulates the inflow of hotregenerated catalyst to the bottom of riser 10. The temperature of theregenerated catalyst is above the control temperature in the riser sothat the incoming catalyst contributes heat to the cracking reaction.The riser pressure is between about 10 and about 35 psig. Between about0 and about 5 percent of the oil charge to the riser can be recycled.The residence time of both hydrocarbon and catalyst in the riser is verysmall and ranges from about 0.5 to about 5 seconds. The velocity throughthe riser is about 35 to about 55 feet per second and is sufficientlyhigh so that there is little or no slippage between the hydrocarbon andthe catalyst flowing through the riser. Therefore no bed of catalyst ispermitted to build up within the riser whereby the density within theriser is very low. The density within the riser is a maximum of about 4pounds per cubic foot at the bottom of the riser and decreases to about2 pounds per cubic foot at the top of the riser. Since no dense bed ofcatalyst is permitted to build up within the riser, the space velocitythrough the riser is unusually high and will have a range between about100 to about 120 and about 600 weight of hydrocarbon per hour perinstantaneous weight of catalyst in the reactor. No significant catalystbuildup within the reactor is permitted to occur, and the instantaneouscatalyst inventory within the riser is due to a flowing catalyst to oilweight ratio betwen about 4:1 and about 15:1, the weight ratiocorresponding to the feed ratio.

The hydrocarbon and catalyst exiting from the top of each riser ispassed into a disengaging vessel 44. The top of the riser is capped at46 so that discharge occurs through lateral slots 50 for properdispersion. An instantaneous separation between hydrocarbon and catalystoccurs in the disengaging vessel. The hydrocarbon which separates fromthe catalyst is primarily gasoline together with some heavier componentsand some lighter gaseous components. The hydrocarbon effluent passesthrough cyclone system 54 to separate catalyst fines contained thereinand is discharged to a fractionator through line 56. The catalystseparated from hydrocarbon in disengager 44 immediately drops below theoutlets of the riser so that there is no catalyst level in thedisengager but only in a lower stripper section 58. Steam is introducedinto catalyst stripper section 58 through sparger 60 to remove anyentrained hydrocarbon in the catalyst.

Catalyst leaving stripper 58 passes through transfer line 62 to aregenerator 64. This catalyst contains carbon deposits which tend tolower its cracking activity and as much carbon as possible must beburned from the surface of the catalyst. This burning is accomplished byintroduction to the regenerator through line 66 of approximately thestoichiometrically required amount of air for combustion of the carbondeposits. The catalyst from the stripper enters the bottom section ofthe regenerator in a radial and downward direction through transfer line62. Flue gas leaving the dense catalyst bed in regenerator 64 flowsthrough cyclones 72 wherein catalyst fines are separated from flue gaspermitting the flue gas to leave the regenerator through line 74 andpass through a turbine 76 before leaving for a waste heat boiler whereinany carbon monoxide contained in the flue gas is burned to carbondioxide to accomplish heat recovery. Turbine 76 compresses atmosphericair in air compressor 78 and this air is charged to the bottom of theregenerator through line 66.

The temperature throughout the dense catalyst bed in the regenerator isabout 1250° F. (676.7° C.). The temperature of the flue gas leaving thetop of the catalyst bed in the regenerator can rise due to afterburningof carbon monoxide to carbon dioxide. Approximately a stoichiometricamount of oxygen is charged to the regenerator, and the reason for thisis to minimize afterburning of carbon monoxide to carbon dioxide abovethe catalyst bed to avoid injury to the equipment, since at thetemperature of the regenerator flue gas some afterburning does occur. Inorder to prevent excessively high temperature in the regenerator fluegas due to afterburning, the temperature of the regenerator flue gas iscontrolled by measuring the temperature of the flue gas entering thecyclones and then venting some of the pressurized air otherwise destinedto be charged to the bottom of the regenerator through vent line 80 inresponse to this measurement. The regenerator reduces the carbon contentof the catalyst from about 1±0.5 weight percent to about 0.2 weightpercent or less. If required, steam is available through line 82 forcooling the regenerator. Makeup catalyst is added to the bottom of theregenerator through line 84. Hopper 86 is disposed at the bottom of theregenerator for receiving regenerated catalyst to be passed to thebottom of the reactor riser through transfer line 26.

While in FIG. I it has been shown that the novel catalyst compositionherein can be introduced into the system as makeup by way of line 84, itis apparent that the catalyst composition, as makeup, or as freshcatalyst, in whole or in part, can be added to the system at anydesirable or suitable point, for example, in line 26 or in line 14.Similarly, the components of the novel catalyst system need not be addedtogether but can be added separately at any of the respective pointsdefined above. The amount added will vary, of course, depending upon thecharge stock used, the catalytic cracking conditions in force, theconditions of regeneration, the amount of metals present in the catalystunder equilibrium conditions, etc.

The reaction temperature in accordance with the above described processis at least about 900° F. (482° C.). The upper limit can be about 1100°F. (593.3° C.) or more. The preferred temperature range is about 950° F.to about 1050° F. (510° C. to 565.6° C.). The reaction total pressurecan vary widely and can be, for example, about 5 to about 50 psig (0.34to 3.4 atmospheres), or preferably, about 20 to about 30 psig (1.36 to2.04 atmospheres). The maximum residence time is about 5 seconds, andfor most charge stocks the residence time will be about 1.5 to about 2.5seconds or, less commonly, about 3 to about 4 seconds. For highmolecular weight charge stocks, which are rich in aromatics, residencetimes of about 0.5 to about 1.5 seconds are suitable in order to crackmono- and diaromatics and naphthenes which are the aromatics which crackmost easily and which produce the highest gasoline yield, but toterminate the operation before appreciable cracking of polyaromaticsoccurs because these materials produce high yields of coke and C₂ andlighter gases. The length to diameter ratio of the reactor can varywidely, but the reactor should be elongated to provide a high linearvelocity, such as about 25 to about 75 feet per second; and to this enda length to diameter ratio above about 20 to about 25 is suitable. Thereactor can have a uniform diameter or can be provided with a continuoustaper or a stepwise increase in diameter along the reaction path tomaintain a nearly constant velocity along the flow path. The amount ofdiluent can vary depending upon the ratio of hydrocarbon to diluentdesired for control purposes. If steam is the diluent employed, atypical amount to be charged can be about 10 percent by volume, which isabout 1 percent by weight, based on hydrocarbon charge. A suitable butnon-limiting proportion of diluent gas, such as steam or nitrogen, tofresh hydrocarbon feed can be about 0.5 to about 10 percent by weight.

The catalyst particle size (of each of the two components, that is, ofthe catalytically-active component and of the diluent) must render itcapable of fluidization as a disperse phase in the reactor. Typical andnon-limiting fluid catalyst particle size characteristics are asfollows:

Size (Microns) 0-20 20-45 45-75>75

Weight percent 0-5 20-30 35-55 20-40

These particle sizes are usual and are not peculiar to this invention. Asuitable weight ratio of catalyst to total oil charge is about 4:1 toabout 25:1, preferably about 6:1 to about 10:1. The fresh hydrocarbonfeed is generally preheated to a temperature of about 600° F. to about700° F. (316° C. to 371° C.) but is generally not vaporized duringpreheat and the additional heat required to achieve the desired reactortemperature is imparted by hot, regenerated catalyst.

The weight ratio of catalyst to hydrocarbon in the feed is varied toaffect variations in reactor temperature. Furthermore, the higher thetemperature of the regenerated catalyst the less catalyst is required toachieve a given reaction temperature. Therefore, a high regeneratedcatalyst temperature will permit the very low reactor density level setforth below and thereby help to avoid back mixing in the reactor.Generally catalyst regeneration can occur at an elevated temperature ofabout 1250° F. (676.6° C.) or more to reduce the level of carbon on theregenerated catalyst from about 0.6 to about 1.5, generally about 0.05to 0.3 percent by weight. At usual catalyst to oil ratios in the feed,the quantity of catalyst is more than ample to achieve the desiredcatalytic effect and therefore if the temperature of the catalyst ishigh, the ratio can be safely decreased without impairing conversion.Since zeolitic catalysts, for example, are particularly sensitive to thecarbon level on the catalyst, regeneration advantageously occurs atelevated temperatures in order to lower the carbon level on the catalystto the stated range or lower. Moreover, since a prime function of thecatalyst is to contribute heat to the reactor, for any given desiredreactor temperature the higher the temperature of the catalyst charge,the less catalyst is required. The lower the catalyst charge rate, thelower the density of the material in the reactor. As stated, low reactordensities help to avoid backmixing.

The reactor linear velocity while not being so high that it inducesturbulence and excessive backmixing, must be sufficiently high thatsubstantially no catalyst accumulation or buildup occurs in the reactorbecause such accumulation itself leads to backmixing. (Therefore, thecatalyst to oil weight ratio at any position throughout the reactor isabout the same as the catalyst to oil weight ratio in the charge.)Stated another way, catalyst and hydrocarbon at any linear positionalong the reaction path both flow concurrently at about the same linearvelocity, thereby avoiding significant slippage of catalyst relative tohydrocarbon. A buildup of catalyst in the reactor leads to a dense bedand backmixing, which in turn increases the residence time in thereactor, for at least a portion of the charge hydrocarbon inducesaftercracking. Avoiding a catalyst buildup in the reactor results in avery low catalyst inventory in the reactor, which in turn results in ahigh space velocity. Therefore, a space velocity of over 100 to 120weight of hydrocarbon per hour per weight of catalyst inventory ishighly desirable. The space velocity should not be below about 35 andcan be as high as about 500. Due to the low catalyst inventory and lowcharge ratio of catalyst to hydrocarbon, the density of the material atthe inlet of the reactor in the zone where the feed is charged can beonly about 1 to less than 5 pounds per cubic foot, although these rangesare non-limiting. An inlet density in the zone where the low molecularweight feed and catalyst is charged below about 4 pounds per cubic footis desirable since this density range is too low to encompass dense bedsystems which induce backmixing. Although conversion falls off with adecrease in inlet density to very low levels, it has been found theextent of aftercracking to be a more limiting feature than totalconversion of fresh feed, even at an inlet density of less than about 4pounds per cubic foot. At the outlet of the reactor the density will beabout half of the density at the inlet because the cracking operationproduces about a four-fold increase in mols of hydrocarbon. The decreasein density through the reactor can be a measure of conversion.

The above conditions and description of operation are for the preferredfluid bed riser cracking operation. For cracking in the olderconventional fluid bed operation or in a fixed-bed operation, theparticular reaction conditions are well known in the art.

Description of Preferred Embodiments

A number of runs were carried out wherein a number of catalysts wereevaluated for their metals tolerance. Each was heat shocked at 1100° F.(593° C.) for one hour, contaminated with nickel and vanadium byimpregnation with nickel and vanadium naphthenates, followed bycalcination at 1000° F. (538° C.) for 10 hours and a steam treatment at1350° F. (732.3° C.) with about 100 percent steam for 10 hours. Theaverage pore radii were determined after calcination, but before thesteam treatment. Each of the catalysts carried on its surface 5000 ppmof nickel equivalents (3,800 parts per million of nickel and 6,000 partsper million of vanadium).

The "MAT Activity" was obtained by the use of the microactivity testpreviously described. The gas oil employed was described in Table I.

The catalysts used in the tests included GRZ-1 alone and physicalmixtures of GRZ-1 and one of the following diluents:

Meta-kaolin

Attapulgite

Sepiolite

Chrysotile, wherein the weight ratios of GRZ-1 to diluent was 60:40.GRZ-1 is a commercial cracking catalyst containing a high zeolitecontent composited with a refractory metal oxide matrix. Each of theabove naturally-occurring clay minerals is further defined by R. E.Grim, referred to above. The surface properties of each of the above areset forth below in Tables II and III:

                  TABLE II                                                        ______________________________________                                                                         Average                                                 Surface      Pore     Pore                                                    Area,        Volume,  Radius,                                      Catalyst   m.sup.2 /g   cc/g     A                                            ______________________________________                                        GRZ-1      222          0.17     16                                           Chrysotile 22           0.05     45                                           Meta-Kaolin                                                                              10           0.04     80                                           Attapulgite                                                                              66           0.19     58                                           Sepiolite  173          0.40     47                                           ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        Composi-                                                                      tion,              Atta-     Meta-                                            Wt %      Sepiolite                                                                              pulgite   Kaolin                                                                              Chrysotile                                 ______________________________________                                        SiO.sub.2 63.83    58.0      50.2  43.4                                       Al.sub.2 O.sub.3                                                                        1.36     9.3       41.1  *                                          MgO       27.65    8.0       0.52  43.3                                       CaO       0.14     2.0       0.58  *                                          Fe.sub.2 O.sub.3                                                                        0.23     3.0       0.30  *                                          ______________________________________                                         *Remainder water                                                         

The data obtained are tabulated below in Table IV:

                  TABLE IV                                                        ______________________________________                                                        Conver-                                                                       sion,    C.sub.5 +      Hydro-                                                Vol. %   (Gasoline)     gen,                                                  of       Vol. %  Carbon,                                                                              Wt % of                               Run             Fresh    of Fresh                                                                              Wt % of                                                                              Fresh                                 No.  Catalyst   Feed     Feed    Catalyst                                                                             Feed                                  ______________________________________                                        1    GRZ-1*     60.0     37.6    5.2    0.58                                  2    Meta-Kaolin*                                                                             49.4     33.8    3.1    0.34                                  3    Sepiolite* 66.8     44.6    4.2    0.33                                  4    Attapulgite*                                                                             65.8     43.7    4.0    0.30                                  5    Chrysotile*                                                                              70.0,    46.3    5.7    0.47                                  ______________________________________                                         *GRZ-1 diluted with indicated additive. Resultant catalyst contained GRZ1     and diluent in a weight ratio of 60:40. All catalysts contaminated with       5000 parts per million of nickel equivalents.                            

The unusual results obtained by operation of a catalytic crackingprocess using the novel catalyst composition defined herein are seenfrom the data in Table IV. Thus, in Run No. 1, wherein the process wasoperated with a commercially available high-activity catalyst, which hasexcellent metals tolerant characteristics when used in catalyticcracking of hydrocarbonaceous feeds, excellent results were obtained,even with the catalyst carrying 5000 ppm nickel equivalents. When in RunNo. 2, the zeolite catalyst of Run No. 1 was diluted with meta-kaolin ina weight ratio of 60:40, following the teachings of U.S. Pat. No.4,289,605 of Bartholic, inferior results were obtained compared withthose obtained in Run No. 1, in that conversion was reduced to 49.4percent, with a drop in gasoline production. However, when the zeoliticcatalyst was combined with clays containing magnesium oxide in each ofRuns Nos. 3 to 5, conversions and amounts of gasoline were better thanthe results obtained in Run No. 1. This is surprising, in that thediluents used in Runs Nos. 3 to 5 do not contain zeolite, and yet when aportion of the catalytically active component was replaced with suchdiluent, excellent results were still obtained.

An additional series of runs was carried out similarly to Runs Nos. 1 to5 above wherein catalyst composition mixtures were employed containing60 weight percent of GRZ-1 and 40 weight percent of diluent. In RunsNos. 6 to 10, the catalyst compositions used carried 1.0 weight percentvanadium, respectively, on their surfaces. Vanadium was deposited on thecatalyst composition surfaces using vanadium naphthenate following theprocedure of Runs Nos. 1 to 5. The data obtained are tabulated below inTable V.

                  TABLE V                                                         ______________________________________                                                        Conver-                                                                       sion,    C.sub.5 +                                                                             Hydro-                                                       Vol. %   (Gasoline)     gen,                                                  of       Vol. %  Carbon,                                                                              Wt % of                               Run             Fresh    of Fresh                                                                              Wt % of                                                                              Fresh                                 No.  Catalyst   Feed     Feed    Catalyst                                                                             Feed                                  ______________________________________                                        6    GRZ-1*     57.0     40.0    2.5    0.20                                  7    Meta-Kaolin*                                                                             51.0     37.5    2.3    0.16                                  8    Sepiolite* 66.2     45.7    3.6    0.15                                  9    Attapulgite*                                                                             62.0     42.8    3.2    0.13                                  10   Chrysotile*                                                                              65.0     43.1    3.7    0.22                                  ______________________________________                                         *GRZ-1 diluted with indicated additive. Resultant catalyst contained GRZ1     and diluent in a weight ratio of 60:40. All catalysts contaminated with       10,000 parts per million of nickel equivalents.                          

The advantages of operating a catalytic cracking process using the novelcatalyst herein are further apparent from the data in Table V. It can beseen from Table V that even when the catalyst composition herein carriedup to 1 weight percent vanadium (10,000 ppm vanadium) in Runs Nos. 8 to10, the level of conversion and the amount of gasoline produced wasstill high. Comparable runs with GRZ-1 alone or GRZ-1 in combinationwith meta-kaolin produced inferior results.

Obviously many modifications and variations of the invention, as hereinabove set forth, can be made without departing from the spirit and scopethereof and, therefore, only such limitations should be imposed as areindicated in the appended claims.

We claim:
 1. A novel catalytic cracking composition comprising acracking catalyst having high activity and, as a separate and distinctentity, a diluent selected from the group consisting of a magnesiumcompound and a magnesium compound in combination with a heat-stablemetal compound, said diluent having a surface area of about 30 to about1000 m² /gram and a pore volume of about 0.05 to about 2.5 cc/gram. 2.The novel catalytic cracking composition of claim 1 wherein said diluenthas a surface area of about 50 to about 600 m² /gram and a pore volumeof about 0.1 to about 1.5 cc/gram.
 3. The novel catalytic crackingcomposition of claim 1 wherein said diluent has an average pore radiusof about 10 to about 200 A.
 4. The novel catalytic cracking compositionof claim 2 wherein said diluent has an average pore radius of about 20to about 110 A.
 5. The novel catalytic cracking composition of claim 1wherein said diluent is a magnesium compound.
 6. The novel catalyticcracking composition of claim 1 wherein said diluent is magnesium oxide.7. The novel catalytic cracking composition of claim 1 wherein saiddiluent is chrysotile.
 8. The novel catalytic cracking composition ofclaim 1 wherein said diluent is attapulgite.
 9. The novel catalyticcracking composition of claim 1 wherein said diluent is sepiolite. 10.The novel catalytic cracking composition of claim 1 wherein said diluentis hectorite.
 11. The novel catalytic cracking composition of claim 1wherein said diluent is a magnesium-containing clay mineral.
 12. Thenovel catalytic cracking composition of claim 1 wherein said diluentcontains a magnesium compound and up to about 90 weight percent of aheat-stable metal compound.
 13. The novel catalytic cracking compositionof claim 1 wherein said diluent contains a magnesium compound and up toabout 50 weight percent of a heat-stable metal compound.
 14. The novelcatalytic cracking composition of claim 12 wherein said heat-stablemetal compound is at least one metal oxide of silicon, aluminum, iron,calcium, phosphorus, boron or zirconium.
 15. The novel catalyticcracking composition of claim 13 wherein said heat-stable metal compoundis at least one metal oxide of silicon, aluminum, iron, calcium,phosphorus, boron or zirconium.
 16. The novel catalytic crackingcomposition of claim 1 wherein the weight ratio of said crackingcatalyst to diluent is in the range of about 10:90 to about 90:10. 17.The novel catalytic cracking composition of claim 1 wherein the weightratio of said cracking catalyst to diluent is in the range of about50:50 to about 70:30.
 18. The novel catalytic cracking composition ofclaim 1 wherein said cracking catalyst has a MAT activity above about1.0.
 19. The novel catalytic cracking composition of claim 1 whereinsaid cracking catalyst has a MAT activity of about 1.0 to about 4.0. 20.The novel catalytic cracking composition of claim 1 wherein saidcracking catalyst is an amorphous silica-alumina catalyst.
 21. The novelcatalytic cracking composition of claim 1 wherein said cracking catalystis a cross-linked clay.
 22. The novel catalytic cracking composition ofclaim 1 wherein said cracking catalyst is a syntheticmica-montmorillonite.
 23. The novel catalytic cracking composition ofclaim 1 wherein said cracking catalyst contains a crystallinealuminosilicate.
 24. The novel catalytic cracking composition of claim 1wherein said cracking catalyst contains a stabilized hydrogencrystalline aluminum silicate.
 25. The novel catalytic crackingcomposition of claim 1 wherein said cracking catalyst contains a rareearth-exchanged crystalline aluminum silicate.
 26. The novel catalyticcracking composition of claim 1 wherein said cracking catalyst comprisesfrom about ten to about 60 weight percent of a zeolite having crackingcharacteristics dispersed in a refractory metal oxide matrix.
 27. Thenovel catalytic cracking composition of claim 1 wherein said crackingcatalyst comprises from about ten to about 40 weight percent of azeolite having cracking characteristics dispersed in a refractory metaloxide matrix.
 28. The novel catalytic cracking composition of claim 1wherein said cracking catalyst comprises from about 20 to about 40weight percent of a zeolite having cracking characteristics dispersed ina refractory metal oxide matrix.
 29. The novel catalytic crackingcomposition of claim 26 wherein the zeolite is a synthetic faujasite.30. The novel catalytic cracking composition of claim 26 wherein thezeolite is at least one synthetic faujasite selected from the groupconsisting of type Y and type X.
 31. The novel catalytic crackingcomposition of claim 30 wherein the X and Y zeolites are rare earthexchanged.
 32. The novel catalytic cracking composition of claim 26wherein the matrix is substantially crystalline.
 33. The novel catalyticcracking composition of claim 26 wherein the matrix is substantiallyamorphous.